There are regulatory requirements for modem aircraft which require the containment of a fire created by a source within a power plant installation. The most obvious instance is of a fire created in an aircraft propulsion system, such as a gas turbine engine. Commercial aircraft propulsion systems are generally required to include a fire seal that is capable of containing and isolating a fire, not only from other propulsion system components (e.g., nacelles and engine fairings), but also from areas surrounding the propulsion system (e.g., wing struts and fairings). Currently, there are a number of disadvantages associated with known fire seals.
By way of example, FIG. 1 shows a gas turbine propulsion system 16 that includes a primary exhaust nozzle 18 connected to the aft end of a gas generator 20 that is housed in an inner shell or casing 20. Thrust reverser components or other various outer structures 24 surround portions of the inner casing 22 and nozzle 18. Typically, an aft engine mount (see FIG. 9, item 92) is located in this region for attaching the propulsion system to a support structure 26, e.g., a wing strut or pylon. In the example of FIG. 1, a fire zone 28 exists generally within the inner shell 22 and at the primary nozzle 18. A fire seal, such as seal 30 shown in FIGS. 1 and 2, is connected to an upper region of the nozzle and is oriented to inhibit flame from spreading aft of the generator or outward to the surrounding structures. The fire seal 30 forms a barrier across the upper area of the exhaust nozzle 18, roughly at the intersection of the nozzle and the support structure 26. In FIG. 1, this intersection is generally within the circle designated by the number 27.
One known fire seal arrangement is shown in FIG. 2, and due to its shape, is called a "turkey feather" fire seal 40. The turkey feather seal 40 consists of a circumferential sheet metal spring 42 formed of segmented steel "fingers" overlapped and attached to a primary exhaust nozzle body 44. Typically, a nozzle fairing 46 is included at a downstream location. The turkey feather fire seal 40 compresses against the lower surface of the support structure 26 and the outer structure 24 when the propulsion system is fully installed. The metal spring 42 is angled upward and then downward, in the forward direction, to provide a solid barrier so that flame cannot pass to downstream locations. This fire seal 40 thus protects the support structures, the wing structures, the surrounding fairings, and the aircraft fuselage from fire emanating from the gas generator, e.g., through an annular area the inner shell and exterior generator surface. (See also FIG. 9.)
There are a number of disadvantages in using turkey feather fire seals 40 in propulsion systems operating in high temperature and/or constant vibration environments. One disadvantage is the possibility of annealing of the seal 40, which can lessen the hard contact sealing force between the nozzle 18 and the support structure 26 and/or outer structure 24. A second disadvantage is potential wear at the seal contact surface due to any relative motion between components. Relative motion can occur due to such circumstances as high sonic vibrations or large relative thermal growth of adjacent components. Because the metal springs 42 are rounded at their contact edge, wear tends to concentrate across a contact line instead of a larger flat surface. The seals 40 can become very sharp as they wear through, causing a potential hazard to surrounding components and/or to maintenance crew.
There exists a need for an installation fire seal that does not allow flame to pass from one location to another and cause an additional fire hazard. Such a seal should ideally be highly reliable, especially in hostile operating environments, such as those found in propulsive systems. In particular, such an ideal aircraft, industrial, or power generation installation fire seal should be unaffected by high temperatures, vibrations, and relative motion between components. The present invention is directed to fulfilling this need.